Not applicable.
Not applicable.
The invention is directed to die casting processes and, more particularly, to die casting processes which use information derived from an analysis of a previously manufactured die casting to modify the process when producing a subsequent die casting. By modifying one or more physical parameters of the die casting process, those conditions which caused the previously manufactured die casting to be unacceptable may be ameliorated. As a result, the likelihood that the subsequently manufactured die casting would be acceptable for use is increased.
Generally, die castings are produced by forcing a molten metal under pressure into a steel die and maintaining the molten metal under pressure until solidification of the molten metal into a casting is complete. A wide variety of metal and metal alloys may be used in die casting processes. For example, aluminum alloys, brass alloys and zinc alloys are all commonly used in die casting processes to form die castings. Broadly speaking, a die casting process requires the following elements: (a) a die-casting machine to hold a molten metal or metal alloy under pressure; (b) a metallic mold or die capable of receiving the molten metal or metal alloy and designed to permit easy and economical ejection of the solidified metal or metal alloy die casting; and (c) a metal or metal alloy which, when solidified into a metal or metal alloy die casting, will produce a satisfactory product with suitable physical characteristics.
There are two types of die-casting machines commonly in use today. The first, or cold-chambered, die-casting machine forces the molten metal or metal alloy into the die by means of a plunger and chamber located outside the molten metal or metal alloy bath. Conversely, the second, or hot-chambered, die-casting machine forces the molten metal or metal alloy into the die by means of a cylinder and piston which are submerged in the molten metal or metal alloy bath. Depending on the production requirements therefore, the metallic mold or dies to be used in die casting processes may be constructed in different styles. A xe2x80x9csinglexe2x80x9d die contains an impression of only one part; a xe2x80x9ccombinationxe2x80x9d die contains an impression of multiple parts; a xe2x80x9cmultiplexe2x80x9d die contains two or more impressions of a single part; and a xe2x80x9ccombination-multiplexe2x80x9d die contains a number of impressions of each one of two or more parts. Single dies are comparatively cheap and, since they reduce the tool investment to a minimum for any one part, are typically used for small lot productions. When properly designed, combination dies will reduce the total die cost for a given set of die castings to a minimum. They are particularly useful for die castings that will always be used in the same quantities and formed of the same alloy. Multiple dies are usually slower to operate than single dies but will give higher production rates for the same labor costs.
It should be readily appreciated that a wide variety of die castings may be produced by application of conventional die casting manufacturing principles. One such die casting is an aluminum alloy die casting. Similarly, while aluminum alloy die castings may be used in a wide variety of applications, in one such application, specially shaped aluminum alloy die castings are used as the rocker cover and the rocker housing for the FL Series motorcycle currently manufactured by the Harley-Davidson Motor Company of Milwaukee, Wis. To enhance the appearance thereof, prior to mounting of the rocker cover and rocker housing die castings on the FL Series motorcycle, the aluminum alloy die castings are plated with chromium. Traditionally, the aluminum alloy die castings have been manufactured at a first facility and subsequently shipped to a second facility for plating.
A drawback to this process has been that, once subjected to the chrome-plating process, the aluminum alloy die castings produced at the first facility often proved unsuitable for their intended later use. For example, using conventional die casting techniques, chrome-plated aluminum alloy die castings to be used as either a rocker cover or rocker housing for the aforementioned FL Series motorcycles were experiencing a rejection rate of about 40% due to defects noted during inspections of the die castings conducted during and/or after the chrome-plating process. While the rejection rate has been attributed to a variety of causes, one such cause is that a number of the various types of defects which commonly occur during the manufacture of an aluminum alloy die casting can remain unnoticed until after an attempt has been made to chrome-plate the die casting.
It should be readily appreciated that a rejection rate of about 40% adds considerably to the cost of chrome-plated aluminum alloy rocker covers or chrome-plated aluminum alloy rocker housings. It should also be readily appreciated that substantial cost savings may be achieved by reducing the rejection rate of chrome-plated aluminum alloy rocker covers, chrome-plated aluminum alloy rocker housings and other products manufactured using die casting processes which are currently plagued by high rejection rates. Achieving a reduction in such rejection rates is, therefore, an object of the present invention
The invention is directed to die casting processes which use information derived from an analysis of a previously manufactured casting to modify the process producing a subsequent casting. By modifying one or more physical parameters of the die casting process, those conditions which caused the prior casting to be unacceptable may be ameliorated. As a result, the likelihood that the subsequent casting would be acceptable for use is increased. In accordance with the teachings of the present invention, a set of conditions for the manufacture of castings are selected and a first series of castings are manufactured under the selected set of conditions. Subsequent to the manufacture thereof, defects in the first series of castings are identified. Based upon the identified defects in the first series of castings, the selected set of conditions are modified and a second series of castings then manufactured under the modified set of conditions.
In one aspect of the invention, the level of each one of the selected set of conditions are measured and each one of the castings marked with a unique identifier during the manufacture of the first series of castings. In another, a first one of the identified defects in the first series of castings is associated with the level of each one of the selected set of conditions during manufacture of a casting having the first one of the identified defects. Based upon this association between the identified defect with the level of the selected set of conditions during the manufacture of the casting having the identified defect, one of the selected set of conditions are identified as in need of modification. The level of the identified one of the selected set of conditions is then modified.
In another aspect of the invention, each one of the first series of castings are marked with a date of manufacture and a serial number. In another, each one of the first series of castings are marked with a date of manufacture, a serial number and a die cast machine number. In still another, the castings are manufactured from aluminum or an aluminum allow at a first location and the defects are identified during an inspection of the castings after they are chrome plated at a second location remotely located relative to the first location.